1. Field of the Invention
The present invention is directed to novel methods of placing concrete compositions where the concrete does not develop undesirable properties when mixed for extended periods and/or pumped to an elevation above a concrete delivery point.
2. Description of the Prior Art
In the formulation of concrete compositions, it is known in the art to use mixtures of different hydraulic cements, as well as other additives such as accelerators and retarders in order to provide desirable properties such as slump, setting times, strengths, and volume changes in order to meet the needs or demands of various specialty applications.
Light weighting aggregates used in concrete compositions include expanded shale, clay and slate, and can range from the so-called “super light weights” which can be used in making concrete weighing 15 to 20 pounds per cubic foot to the natural aggregates and finally to the expanded shale, clay and slate aggregates which can produce structural concrete ranging from about 85 to 115 pounds per cubic foot when produced by the rotary kiln method and from about 90 to 120 pounds per cubic foot when produced by sintering. Structural light weight concrete is described as having a 28 day compressive strength of at least 2,500 pounds per square inch and an air dry weight of no more than 115 pounds per cubic foot. Weights can be increased by replacing a portion of the light weight aggregate with sand.
Other light weight aggregates used in concrete compositions are disclosed in U.S. Pat. No. 3,600,476 (light weight aggregates from fly ash and sludge); U.S. Pat. No. 3,661,604 (light weight aggregate mixture derived from clay, sand and crushed bricks); U.S. Pat. No. 4,504,320 (light weight aggregate containing fly ash, silica fume and microspheres); and U.S. Pat. No. 4,741,782 (light weight aggregate pellets from fly ash, cement and silica fume dust).
Often, when the above-described light weight aggregates are used in concrete formulations that are subsequently mixed for extended periods and/or pumped to an elevation above a concrete delivery point, the concrete formulation demonstrates a drop in fluidity often referred to as slump loss.
In many cases, dispersants are added to concrete formulations in an attempt to improving the fluidity of light weight concrete compositions. However, the water in the concrete composition tends to be adsorbed into the light weight aggregate during extended mixing and/or under the pressure generated during pumping resulting in a highly reduced water content resulting in slump loss, additionally, air is forced out of the concrete, the combination of which gives rise to the problems of poor workability and applicability.
Further, when dispersants are used to prevent slump loss, their ability to reduce the slump loss varies and becomes weaker with time and also causes significant and often undesirable set retardation.
U.S. Pat. Nos. 3,214,393, 3,257,338 and 3,272,765 disclose concrete mixtures that contain cement, a primary aggregate, particulate expanded styrene polymer, and a homogenizing and/or a surface-active additive.
U.S. Pat. No. 3,021,291 discloses a method of making cellular concrete by incorporating into the concrete mixture, prior to casting the mixture, a polymeric material that will expand under the influence of heat during curing. The shape and size of the polymeric particles is not critical.
U.S. Pat. No. 5,580,378 discloses a lightweight cementitious product made up of an aqueous concrete composition that can include fly ash, Portland cement, sand, lime and, as a weight saving component, micronized polystyrene particles having particle sizes in the range of 50 to 2000 μm and a density of about 1 lb/ft3. The mixture can be poured into molded products such as foundation walls, roof tiles, bricks and the like. The product can also be used as a mason's mortar, a plaster, a stucco or a texture.
JP 9 071 449 discloses a lightweight concrete that includes Portland cement and a lightweight aggregate such as foamed polystyrene, perlite or vermiculite as a part or all parts of the aggregate. The foamed polystyrene has a granule diameter of 0.1-10 mm and a specific gravity of 0.01-0.08.
U.S. Pat. Nos. 5,580,378, 5,622,556, and 5,725,652 disclose lightweight cementitious products made up of an aqueous concrete composition that includes cement and expanded shale, clay, slate, fly ash, and/or lime, and a weight saving component, which is micronized polystyrene particles having particle sizes in the range of 50 to 2000 μm, and characterized by having water contents in the range of from about 0.5% to 50% v/v.
U.S. Pat. No. 4,265,964 discloses lightweight compositions for structural units such as wallboard panels and the like, which contain low density expandable thermoplastic granules; a cementitious base material, such as, gypsum; a surfactant; an additive which acts as a frothing agent to incorporate an appropriate amount of air into the mixture; a film forming component; and a starch. The expandable thermoplastic granules are expanded as fully as possible.
WO 98 02 397 discloses lightweight-concrete roofing tiles made by molding a hydraulic binder composition containing synthetic resin foams as the aggregate and having a specific gravity of about 1.6 to 2.
WO 00/61519 discloses a lightweight concrete that includes a blend of from around 40% to 99% of organic polymeric material and from 1% to around 60% of an air entraining agent. The blend is used for preparing lightweight concrete that uses polystyrene aggregate. The blend is required to disperse the polystyrene aggregate and to improve the bond between the polystyrene aggregate and surrounding cementitious binder.
WO 01/66485 discloses a lightweight concrete composition containing by volume: 5 to 80% cement, 10 to 65% expanded polystyrene particles; 10 to 90% expanded mineral particles; and water sufficient to make a paste with a substantially even distribution of expanded polystyrene after proper mixing.
U.S. Pat. No. 6,851,235 discloses a building block that includes a mixture of water, cement, and expanded polystyrene (EPS) foam beads that have a diameter from 3.18 mm (⅛ inch) to 9.53 mm (⅜ inch) in the proportions of from 68 to 95 liters (18 to 25 gallons) water; from 150 to 190 kg (325 to 425 lb) cement; and from 850 to 1400 liters (30 to 50 cubic feet) prepuff beads.
U.S. Pat. No. 5,913,791 discloses a building block that has a cement-based attachment layer on one or both exterior surfaces of the block that receives and holds a penetrating fastener such as a nail, screw, staple, or the like. One cement-based layer contains water, cement, and expanded polystyrene foam beads in first proportions and a second exterior surface contains water, cement, and expanded polystyrene foam beads in second proportions different than the first proportions.
In many cases, water is able to adsorb or absorb into and/or onto the expanded polystyrene particles leading to a highly reduced water content in the concrete composition, slump loss, poor workability and applicability after extended mixing and/or under the pressure generated during pumping as described above.
In many situations where expanded polystyrene particles are used in concrete formulations, the expanded polystyrene particles lower the strength and/or structural integrity of concrete compositions. Further, concrete articles made from prior art expanded polystyrene particles have at best inconsistent physical properties, such as Young's modulus, thermal conductivity, and compressive strength, and typically demonstrate less than desirable physical properties.
Thus, there is a need in the art to provide methods for light weighting concrete that do not result in slump loss and set retardation.